The following study of pre-war Japanese parties shows how the amount of influence parties have on government itself affects their behaviour. The way in which parties act is commonly seen to result largely from such factors as the class structure of the society, its racial and religious composition, and whether the voting population is primarily rural or urban. While this study does not deny the importance of such factors, it concentrates m6re on the constitutional arrangement of government, that is, the way in which governing power is distributed among politically influential institutions. Under the 1890 Meiji Constitution, governing power was shared among seven separate institutions, each of which was independent of the others and received regular representation in the Cabinet. Only one of these institutions con­ tained popularly elected men belonging to political parties, and when the balance of power among the institutions varied, the characteristics of the parties varied also. Three types of parties, corresponding to three different patterns of the institutional balance, were identified according to the following categories: rivalry between parties, their internal discipline, programmes, and types of leaders. All these varied directly with changes in the degree of party influence on government. The influence of the constitutional arrangement on the way in which parties act has so far received little attention from political scientists. My study attempts to correct this under emphasis by showing how the Meiji Constitution helped shape prewar Japanese parties.